The present invention is concerned with pressure-sensitive carbon-copying materials, also known as chemical copying papers, such copying papers commonly being provided with a color-forming coating and a color substance-accepting coat. Under pressure, part of the color-former reacts with the color-substance acceptor under local discoloration.
Such copy papers contain, in most cases, organic compounds which are enclosed in micro-capsules, and which are commonly known as color-formers since, in combination with color-substance acceptors, they produce a color-reaction. Such color formers include, for example, crystal violet lactone, malachite green lactone, benzoyleucomethylene blue, rodamin beta lactume or leucoauramine. Color substance acceptors which are presently in use include, for example, those having a base of attapulgite, zeolite, kaolin, phenol resins, as well as phenol compounds with freely reacting phenol groups in combination with binding agents. Such binding agents may include, for example, polyvinyl, polyvinyl chloride and polyvinyl acetate compounds and mixed polymerizates of these compounds and resins, for example, ester-derivatives of colophony and alcohol, as well as metal stearates and silicic acid. Commonly, the color-formers and color-substance acceptors are present in separate layers. Such a paper may, however, also comprise a sheet which contains color-forming agents as well as color-substance acceptors, possibly with an intermediate layer. Under pressure, a part of the color-former reacts with the color-substance accepting-mass under local discoloration.
It has been found that the color-substance acceptor masses which are utilized in chemical copying papers can be improved in many respects by adding to these masses chlorides of metal salts, sometimes in combination with urea or urea-derivatives as the chief reacting components.
The utilization of metal chlorides will result in an intensive color formation which is characterized by a special light-stability, so that this color formation is obtained with color-forming coats which are not as thick as the acceptor-layers, in which are present predominantly the common color-substance acceptors, such as attapulgite or kaolin.
Accordingly, the present invention is concerned with a pressure-sensitive copying material based on a color-forming mass and a color-substance accepting mass which reacts when coming in contact with said color-forming mass to produce color, and characterized in that the color-substance accepting mass contains as reaction components a chloride of a metal having an atomic weight of from 50-66, the metal preferably being zinc, vanadium, chromium, manganese, iron, cobalt, nickel or copper, possibly in combination with urea or its derivatives, for example thiocarbamine. Also present are a binding agent and other additives. The metal salt is bound to the base material directly in combination with the binding agent, and the color-forming mass comprises an initial dyestuff product which is also combined directly with the binding agent, and which reacts with the color-substance acceptor during color-formation.
The color-substance accepting mass can be applied to the base with the aid of a solvent in which the metal chloride, or the combination metal-chloride and urea which is to be used, or a derivative thereof, is insoluble, or is applied also in the form of a fluid solution. In the latter case, the metal-chloride, or the combination to be utilized, may be dispersed in wax and applied at a temperature of from 50.degree.-220.degree. C. The waxes which may be utilized may be vegetable, animal- or mineral-waxes, synthetic and chlorinated waxes, as well as paraffins, oxide-waxes, polyethylene- and polyethylene-oxide waxes having a molecular weight of 400-12000.
In the application of the solvent, there may be used aliphatic hydrocarbons, chloro-hydrocarbons, aromatic hydrocarbons, alcohols, esters or ketones.
Additionally, suitable binding agents for the coating application are polyvinyl-, polyvinyl chloride- and polyvinyl acetate compounds, or a mixed polymerizate of these compounds to which may be added softening agents, metal stearates such as cobalt or zinc stearates, natural resins or additional synthetic resins, and conditionally active or inactive clay, for example kaolin or silicic acid. As urea derivatives, one may utilize thiocarbamine or any random derivative of the common formula: EQU C.sub.p H.sub.4 +.sub.q R
in which
p=1-20, q=1-16 and, PA1 R=a member of the group N.sub.2 O, N.sub.2 O.sub.2, N.sub.2 S or N.sub.4 O.sub.3, or a complex compound with halogen, especially a trifluoride or trichloride urea complex compound.
Urea as well as thiocarbamine, and especially diphenylthiocarbamine should be mentioned as an additive for the metal chloride.
It has also been noted that the addition of a metal stearate or a mixture of acid and alcohol on an acetylene base with cycloaliphatic N- or O-containing condensation-products results in an intensification of the color reaction. As to the stearates utilized in the copying materials of the present invention, in addition to the cobalt and zinc stearates, there may also be utilized stearates of lead, tin, calcium, aluminum, barium or iron.
It is common in the prior art to also add metal salts to the color-substance accepting masses. However, these components should be added only in small quantities, in order to accelerate the color-format ion and not for the purpose of producing the actual color-reaction. In the present compositions, the metal salts, especially the zinc-chloride or the combination of zinc-chloride and urea or its derivatives, are added in an amount of about 5-90% in weight. The ratio of the mixture of metal chloride and urea or its derivatives should preferably be from about 5:1 to 1:1.
Zinc chloride is especially suitable as the metal chloride. However, excellent color-intensive and color-stable copies are also obtained with other chloride such as, for example, chromium (III) chloride, manganese (II) chloride, iron (III) chloride, nickel (II) chloride, cobalt (II) chloride or copper (II) chloride.
In the case where zinc chloride and urea are utilized for the color-substance accepting mass, a ratio of these substances of about 9:1 to 1:5 is advantageously employed.
The present invention produces not only the advantage of obtaining the above listed color-intensive and color-true transfer pictures, but it also produces the possibility for applying the color-substance accepting mass in a substantially thinner coating than has been formerly possible. The color-substance accepting mass may be applied in a quantity of from 2-5 g/m.sup.2. It is, however, a special effect of the present invention that an application of only 0.5-6 g/m.sup.2, preferably 0.3-4 g/m.sup.2 suffices, without causing a reduction of the quality of the copies. Such thin layers of application result in the advantage that substantially more sheets may be used in a set of copying-papers than was formerly possible. The preferred thickness of application depends on the type of the coating method or on the type of the solution- or dispersing-material used. If water is utilized as the dispersing-agent, then the applied coats are somewhat thicker than in the use of organic solvents, such as acetone or ethyl alcohol.